In his final months in office, President Barack Obama sought to lock in a structure and set of rules governing targeted killings and drone strikes so that the in­cred­ibly lethal tool would not be abused by his successors.

In his first six weeks in office, President Trump, who has made destroying the Islamic State his top foreign policy priority, has pressed to roll back some of those checks.

The Trump administration is close to finishing a review that would make it easier for the Pentagon to launch counterterrorism strikes anywhere in the world by lowering the threshold on acceptable civilian casualties and scaling back other constraints imposed by the Obama administration, senior U.S. officials said.

The ongoing review, which is being considered at senior levels of the National Security Council, would undo a series of rules that Obama imposed, beginning in 2013, to rein in drone operations outside active war zones.

The Trump review must still be approved by the president, but recent drafts of the new policy would represent a major change in the way the United States approaches drone strikes and other targeted-killing operations in places such as Yemen, Somalia and Libya.

The changes to the Obama-era Presidential Policy Guidance would empower the Pentagon to make decisions on targets without approval from the White House and potentially scrap the “near-certainty” standard of no civilian deaths for strikes outside war zones. The Trump plans are also likely to relax the requirement that potential terror targets pose a “continuing and imminent threat” to U.S. personnel, officials said.

A senior administration official said that the Trump White House remained committed to a standard above the minimum requirement mandated by the international law of armed conflict that governs most military operations.

“Some standard above [that] is wise,” the official said.

Obama imposed the restrictive rules because he was worried that future administrations might be seduced by the power of drones to destroy potential threats to the United States at a very low cost in both blood and taxpayer dollars anywhere in the world.

He also hoped that his policy would provide a check internationally as armed drones proliferate, to countries such as China or Iran.

“We have to create an architecture for this because [of] the potential for abuse,” Obama said in August during a speech. At the time, Obama said one of his goals before leaving office was to create an “internal structure” and “institutionalized process” that would restrict his successors.

Now it is likely that Trump will move to lift many of those Obama-era restrictions, making it easier for the U.S. military to strike potential terror targets anywhere in the world. Senior U.S. officials said Trump is almost certain to back changes that would shift final approval for individual strikes from the White House back to the Pentagon and the CIA, where they resided before the new rules were imposed.

The current Obama-era constraints require the Defense Department and CIA to provide overall plans for killing or detaining individual high-value terrorism targets to the president for approval. The extra layer of bureaucracy was designed to ensure that the Pentagon and CIA were abiding by the White House-mandated constraints and that there was a consensus within the U.S. government on both the need to kill the target and the potential diplomatic blowback of an errant strike.

But some critics, particularly in the Pentagon and CIA, have said that centralizing the process in the White House created an approval bottleneck that has made it harder to hit potentially fleeting targets who are not already on the White House’s kill list.

“We are seeking ways to accelerate our operations against terror groups, and be more nimble and agile in our speed of response,” said Pentagon spokesman Capt. Jeff Davis. “But we always will maintain a commitment to minimizing, avoiding civilian casualties.”

The move to streamline the process and delegate decision-making would also free up the White House to consider larger issues, such as its overall strategy in places such as Yemen, Libya and Somalia. Those broader strategic discussions under Obamaoften took a back seat to debating and approving terror targets, critics said.

“A big goal is getting the White House out of the way of itself,” said a senior U.S. official, who spoke on the condition of anonymity to discuss internal administration debates. “The president believes too much has been centralized in the White House, and he wants to push decisions down to the agencies.”

The White House is also weighing whether to relax or change the current standard on civilian casualties, which demands near-certainty that no civilians are killed or injured in U.S. raids or drone strikes outside conflict zones.

One possibility being considered could demand a near-certainty that no women or children are killed, but impose a different standard for military-age males. Or the White House could choose to waive the more stringent rules in certain geographical areas for certain periods of time.

But the senior Trump administration official said any new policy will acknowledge that any civilian casualties overseas work against U.S. counterterrorism policy goals. “ We want to have a wise, moral standard that allows us to maintain the consent of the governed in these countries,” the official said.

The Obama White House touted the precision of U.S. drone operations in a report last summer, concluding that a range of 64 to 116 civilians had been killed in drone strikes or other lethal air attacks outside established war zones. Independent groups that track civilian deaths have estimated civilian death rates that are two or three times those figures.

In a letter released Friday, 37 former top U.S. officials, most of whom served in the Obama administration, urged Trump to move cautiously when modifying or overturning restrictions imposed in recent years. On the issue of civilian casualties, the signatories pressed Trump to stick with the current approach.

The final area that the Trump White House seems likely to scrap is a standard that potential terror targets outside war zones pose a continuing and imminent threat to Americans. “It’s not clear whether that’s a reasonable standard,” said a U.S. counterterrorism official who has been involved in the discussions. “Of all the mandates, that might be the most vulnerable.”

Both the Trump and Obama administrations have pursued an approach to counterterrorism that seeks, wherever possible, to work through local indigenous partners. Such a strategy is cheaper and also helps keep American forces out of harm’s way.

But the requirement that U.S. officials prove a continuing and imminent threat to American citizens has made it much harder to provide air or drone support to U.S. allies when they are under fire from groups such as the Islamic State or al-Qaeda in places such as Yemen, Libya and Somalia.

For Obama, the high standard ensured that local partner forces did not come to depend on American air support and that the U.S. military did not inadvertently slide down a slippery slope into larger-scale combat operations or even war.

The downside of such an approach is that it often left beleaguered U.S. allies feeling bitter and betrayed when their far more powerful American partner declined to provide potentially lifesaving assistance.

“How much are we supporting our partners if we are only saying that we will take a strike if there’s a continuing and imminent threat to U.S. persons?” said Luke Hartig, a former senior director for counterterrorism in the Obama administration and a fellow at the New American Foundation.

Said another senior U.S. official: “Essentially we are saying to allies that we’ll only use our fancy tools when it’s our butts on the line.”

The Trump administration has been weighing several alternatives to the continuing-and-imminent-threat standard. One lower standard being considered would require the Pentagon or intelligence agencies to prove that potential targets perform a “key leadership function” for al-Qaeda or an affiliated group. Another possibility would require U.S. officials to demonstrate that the target’s death would result in a “material setback” for the terror group, said the U.S. counterterrorism official.

“There are lots of options to consider here,” the official said.

Greg Jaffe is a national security reporter for The Washington Post, where he has been since March 2009. Previously, he covered the White House and the military for The Post.

Karen DeYoung is associate editor and senior national security correspondent for The Post. In more than three decades at the paper, she has served as bureau chief in Latin America and London and as correspondent covering the White House, U.S. foreign policy and the intelligence community.